By using new molecular virological techniques, Non-A Non-B hepatitis patients have now been categorized into those infected with hepatitis C virus (HCV), a parenterally transmitted flavivirus, and hepatitis E virus (HEV), a fecal-oral transmitted "hepatitis E-like virus." WHO estimates that 170 million are infected with HCV, the most common cause of chronic viral hepatitis (CVH), post-necrotic cirrhosis of the liver and hepatocellular carcinoma (HCC). HEV is primarily transmitted in developing countries where it is the most common cause of acute viral hepatitis (AVH) and fulminating hepatitis, particularly in pregnant women. We and others have documented that the highest prevalence of HCV, and also possibly HEV, in the world occurs in Egypt. We have established a Network of Egyptians and Americans who are studying viral hepatitis and its cost to the country. In this ICIDR proposal, we will extend the work of this Network to include investigations of: (1) the effect that the host genome has on chronicity and cirrhosis following HCV infection (Project 1); (2) the host, viral, and environmental determinants of HCC and (because HCV is lymphotrophic as well as hepatotrophic) non-Hodgkins lymphoma (NHL, Project 2); and the epidemiology and complications of HEV (Project 3). Projects 1 & 2 will have case-control studies. The former will compare: (a) chronic carriers of HCV RNA vs. subjects who clear infection and (b) those with HCV who develop cirrhosis vs. those that show no signs of disease; while the latter compares HCC or NHL cases vs. age- and gender-matched controls. Projects 1-3 will have prospective cohort studies of 10,000 inhabitants of two villages with prevalence of anti-HCV of 9% and 24% and anti-HCV of 51 and 70%, respectively. Their goals will be to determine incidence of, and risk determinants for cirrhosis (Project 1), HCC and NHL (Project 2), and HEV infection and disease (Project 3). A cohort of pregnant women and children will be studied to assess HEV morbidity in pregnancy and exposures and disease in infancy. Domestic animals and peri-domestic rodents will be studied to determine whether HEV has a zoonotic component in Egypt. Viral genotypes, host class I and II alleles and candidate genes, e.g., chemokine receptors and HDL, a possible HCV receptor, and environmental exposures and their impact on host genes (p53 genetic fingerprinting) will be assayed. Because the scientific, administrative, logistic and laboratory network is in place and both HCV and HEV have such a high prevalence in Egypt, these investigations have a high probability of early success. Explanations for these very important questions can be obtained at a fraction of the cost and time as they could be found elsewhere, and the results should lead to the development of better interventions to prevent the two most important causes of liver disease in the world.